Welding is a repair process which is frequently used to close cracks or to apply material. In this case, a laser is often used as the energy source. The laser welding process is also used to repair directionally solidified components, for example turbine blades or vanes of the largest gas turbines, after they have been used, which possibly have cracks as a result of extraordinarily severe loading. These can be components with grains solidified in columnar form (DS) or else single crystals (SX).
The component therefore has a defined preferred crystallographic direction in the crystal structure. The solidification behavior of the material, which should obtain the same orientation as the substrate during the laser welding, depends on the composition of the alloy, the temperature gradient and the solidification rate. For a defined alloy, there are graphs showing how the structure developed depending on the temperature gradient and the solidification rate.
Nevertheless, grains frequently grow in an undesirable direction.